Developing device of the magnetic brush type for electrophotographic apparatus using a dry developer

ABSTRACT

A developing device of the brush type for electrophotographic apparatus using a dry developer comprising pivotal magnet units on whose undersides a magnetic brush composed of powdered dry developer is formed, a developer supplementing pan disposed beneath the magnet units containing a quantity of the dry developer for delivering a fresh supply to the magnet units, a mechanism for relatively moving the pan and the magnet units toward and away from each other, and a photosensitive sheet conveyor interposed between the magnet units and the developer supplementing pan. The conveyor is of the endless belt type and can be moved between a developing position, wherein the endless belt is driven, and a retracted position, wherein the endless belt is stationary, permitting the magnet units and the developer pan unobstructed relative movement while the conveyor is disposed in its retracted position.

United States Patent 091 Koizumi DEVELOPING DEVICE OF THE MAGNETIC BRUSH TYPE FOR ELECTROPHOTOGRAPHIC APPARATUS USING A DRY DEVELOPER [75] Inventor: Yutaka Koizumi, Kanagawa, Japan [73] Assignee: Kabushiki Kaisha Ricoh, Tokyo,

Japan 22 Filed: Dec. 20, 1971 211 Appl. No.: 209,521

[30] Foreign Application Priority Data 2,033,991 3/1936 Meltonetal. "In": ..91/18 1 July 10, 1973 Primary ExaminerMervin Stein Assistant Examiner-Leo Millstein Att0rney-Henry T. Burke et al.

[5 7 ABSTRACT A developing device of the brush type for electrophotographic apparatus using a dry developer comprising pivotal magnet units on whose undersides a magnetic brush composed of powdered dry developer is formed, a developer supplementing pan disposed beneath the magnet units containing a quantity of the dry developer for delivering a fresh supply to the magnet units, a mechanism for relatively moving the pan and the magnet units toward and away from each other, and a photosensitive sheet conveyor interposed between the magnet units and the developer supplementing pan. The conveyor is of the endless belt type and can be moved between a developing position, wherein the endless belt is driven, and a retracted position, wherein the endless belt is stationary, permitting the magnet units and the developer pan unobstructed relative movement while the conveyor is disposed in its retracted position.

10 Claims, 11 Drawing Figures PATENIEDJUHOW 3.744.451

SEEI 1 Bf 7 INVENTOR YU A/(A KO/ZUM/ Ink QM ATTORNEY Pmsmeow 3.144.451

SlEEI 2 0F 7 IN VENTOR YU 774/44 KO/ZUM/ ATTORNEY PAIENIEU JUL 1 0 I975 SHEEI 3 0F 7 INVENTOR V0 74 K4 K0 Zy )MI M ATTORNEY PAIENIE JUL 1 0 ma SHEU I [If 7 yum/ 4 KU/ZU BY i M ATTORNEY PAIENIED JUL 1 0 suzusnri INVENTOR YU/WK/J KO/ZUM/ ATTORNEY PATENIED JUL 1 0 p925 SHEET 7 BF 7 INVENTOR WI/m KO/ZUM/ BY If? M ATTORNEY DEVELOPING DEVICE OF THE MAGNETIC BRUSH TYPE FOR ELECTROPHOTOGRAPHIC APPARATUS USING A DRY DEVELOPER BACKGROUND OF THE INVENTION This invention relates to a developing device of the magnetic brush type for electrophotographic apparatus, such for example as electrophotographic copying machines, electrophotographic plate making machines and the like, which use a dry developer.

In one type of magnetic brush developing method known in the art, a developer is prepared by mixing a toner comprising a synthetic resin in colored powder form with a carrier in the form of iron powder and electrically charging the mixture by friction, and such developer is attracted to a receiving surface by magnets to form a magnetic brush. The magnetic brush so formed is moved relative to the surface of a photosensitive sheet on which an electrostatic latent image has been formed so as to develop and render such electrostatic image visible. This magnetic brush developing method is effective to prevent edge effects and produces a'well-defined, clearly visible image.

Conventional devices for carrying the aforesaid magnetic brush developing method into practice generally comprise the basic components of pivotal magnet units adapted to form on their undersides a magnetic brush composed of a dry developer in powder form; a developer supplementing pan disposed beneath such magnet units and containing therein a quantity of the dry developer in powder form for supplementing the developer on the magnet units; and photosensitive sheet conveyor means interposed between the magnet units and developer supplementing pan.

When such devices are employed, a fresh magnetic brush should be formed on the undersides of the magnet units by a fresh supply of developer from the developer supplementing pan and moved relative to the surface of a photosensitive sheet, each time a duplicate is to be made. Since the developer supplementing pan is disposed below the surface of the photosensitive sheet and the magnetic brush is disposed thereabove, in order to form the fresh magnetic brush it is necessary to move either the developer supplementing pan or the magnets past the conveyor surface when one photosensitive sheet has been moved from the developing position and a next following photosensitive sheet has not yet been delivered to the developing position. This operation makes it extremely difficult to use an endless belt as the photosensitive sheet conveyor means and hence to automate the photosensitive sheet conveying and treating steps.

The present invention obviates the aforementioned disadvantage of the conventional developing devices of the magnetic brush type and permits the automation of the photosensitive sheet conveying step, and hence the duplicating steps of such apparatus.

SUMMARY OF THE INVENTION Accordingly, this invention provides a developing device of the magnetic brush type wherein the photosensitive sheet conveyor means is in the form of an endless belt conveyor which means is movable in its entirety between a developing position and a retracted position so that the magnet units and the developer supplementing pan can be moved in unobstructive relative movements toward or away from each other. This arrangement permits the automating of the photensitive sheet conveying and treating steps. Also, the endless belt conveyor means is moved in the same direction as an exposed photosensitive sheet when moving from its retracted position to its developing position. This permits it to transport photosensitive sheets to the developing position without the need for driving the belt. Preferably, the belt of the endless belt means is not driven till the endless belt means is moved as a whole to the developing position. In such case, it is possible to eliminate troubles which might otherwise be caused by the driving of the belt when the endless beltmeans is withdrawn to the retracted position.

Additional details and features of the present invention are pointed out in the following description of the preferred embodiment thereof which is shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS of FIG. 2;

FIG. 4 is a perspective view of the magnet unit drive means;

FIG. 5A to SF are views illustrating the manner of operation of the developing device according to this invention; and

FIG. 6 is a side view illustrating the developer supplementing pan elevational means.

DETAILED DESCRIPTION OF THE INVENTION An electrophotographic plate making machine with a developing device of the magnetic brush type in accordance with the present invention is shown, in FIG. 1, wherein a photosensitive sheet for producing a master plate is introduced into an electrophotographic plate making machine 1 through sheet feed means 2, uniformly charged at an electrical charging section 3, and moved by means of a belt 5 to an exposing position 6 under the drawing action of a suction box 4, where the photosensitive sheet 13 temporarily remains stationary. When the photosensitive sheet stops at the exposing position 6, exposing light source 7 is tumed on and rays of light from the source 7 are reflected by a reflector 8 and impinge on an original 10 disposed on an original receiving transparent plate 9 which reflects the rays of light. The reflected rays of light are again reflected by a reflector 11 and pass through a movable optical system 12 to reach the exposing position 6, so that the photosensitive sheet 13 standingstill in the exposing position 6 is exposed to an optical image of the original 10 to form an electrostatic latent image of the original thereon. Upon completion of exposure, the photosensitive sheet 13 is moved by belt 5, which is rendered operative again, into a developing section 14 which is constructed, as will presently be described, according to the present invention. In the developing section 14 the electrostatic latent image of the original I it is heated so as to fix the developed image thereon before being discharged from the machine.

The developing section 14 is shown in greater detail in FIG. 2, wherein movable endless belt conveyor means 16 is mounted for horizontal movement in its entirety between a solid line position in which endless belt 16A is driven and transports a photosensitive sheet past magnet units 21 and a dash-and-dot line position in which conveyor means 16 is retracted with endless belt 16A stationary, so as to permit a fresh magnetic brush to be formed.

When conveyor belt means 16 is moved to the solid line position, a drive roller 18 for belt 16A is brought into engagement with a rotation transmission system 17A of an electric motor 17 so as to drive the endless belt about its support rollers 13A. The horizontal movement of endless conveyor belt means 16 can be effected by any known drive and transmission means. For example, during its horizontal movement, endless conveyor belt means 16 may be supported and guided by fixed guide rods 16B (shown in FIG. 3) which are disposed on opposite sides of the conveyor means 16 and which may be provided with a suitable worm gear drive 16C.

A developer supplementing pan 19 is disposed beneath the path of movement of the photosensitive sheets, and two magnet cases 21A each containing a magnet 20 therein are disposed above the path. Developer supplementing pan 19 contains a toner 22 and mounts therein an agitator 23 which is adapted to be driven from outside by drive means 23A.

As shown in FIG. 3 and FIG. 4, the two magnet cases 21A, each containing one magnet 20, are pivotally supported by two parallel shafts 24 through support links 25 and 25. Support links 25 are firmly secured to shafts 24, and support links 25 are loosely fitted over shaft 24. The two shafts 24 are driven from a drive motor 26 through an eccentric wheel 27, a connecting rod 28, a support arm 24A secured to one shaft 24, another connecting rod 29 and another support arm 248 secured to the other shaft 24, so that the shafts 24 may be reciprocatorily rotated in directions opposite to each other. As a result, the two magnet units 21 each comprising a magnet 20 and a magnet case 21A are moved pivotally in opposite directions as shown by arrows F, because the support link 25 for one magnet unit is firmly secured to one shaft 24 and the support link 25 for the other magnet unit is firmly secured to the other shaft 24.

Operation of the developing device according to this invention will be described with reference to FIG. 5. In FIG. A endless belt conveyor means 16 is in the retracted position, and no magnetic brush has been formed on the undersides of the magnet cases 21A. Then, developer supplementing pan 19 is moved upwardly as shown in FIG. 5B, by suitable elevating means 30-36 (shown in detail in FIGS. 3 and 6) and supplies a dry developer 22 to the undersides of the magnet cases 21A so as to form a fresh magnetic brush 21B thereon. After the fresh magnetic brush 21B is formed, developer supplementing pan 1 1' is returned to its initial position as shown in FIG. 5C. At this time, exposure of a photosensitive sheet to an optical image of the original is completed and endless belt 5 begins to move again. The endless belt conveyor means 16 of the developing device 14 also begins to move to its developing position. When the leading end of the photosensitive sheet 13 reaches endless belt conveyor means 16, it is caused to move together with the conveyor means as the latter moves leftwardly in FIG. 5 and is deposited on the belt surface. When endless belt conveyor means 16 reaches the position shown in FIG. 5D, motor 17 is actuated to drive the belt 16A with the photosensitive sheet 13 on its surface so that the photosensitive sheet is moved gradually without interruption past the undersides of the magnet units 21.

As the photosensitive sheet 13 is moved past, the magnet units 21, which are formed on their undersides with the fresh magnetic brush 2113 as aforesaid, are moved in pivotal motion by the drive means shown in FIG. 3 and FIG. 4 so that the dry developer in brush form carried thereon is brought into contact with the photosensitive sheet 13. The electrostatic image on the photosensitive sheet is thereby converted into a visual image. The photosensitive sheet 13 is then moved on to a fixing section 15.

After the developing of the photosensitive sheet is completed and the developed sheet is passed on to the fixing section 15, endless belt conveyor means 16 is retracted as shown in FIG. SE to the dash-anddot line position shown in FIG. 2. Then, the magnet cases 21A of magnet units 21 are moved slightly away from their magnets 20 as shown in FIG. 5F by suitable lowering means 21C indicated in FIG. 4, which may be similar to the pan elevating means shown in FIG. 6. This reduces the magnetic force of the magnets 20 which is exerted on the developer forming the magnetic brush 218 on the undersides of magnet cases 21A, so that the developer 22 drops into developer supplementing pan 19 disposed below magnet cases 21A. Thereafter, the magnet cases 21A are moved toward their magnets 20, to the position shown in FIG. 5A ready for the next cycle.

As aforesaid, developer supplementing pan 19 moves upwardly, to the dash-and-dot line position shown in FIG. 2, (or in the full line position as in FIG. 513) as endless belt conveyor means 16 moves to its retracted position to deliver a fresh supply of dry developer in powder form to magnet units 21. The mechanism for moving developer supplementing pan 19 will be described with reference to FIG. 6.

In FIG. 6, a side plate 30, supporting developer supplementing pan 19, is formed therein with a slot 30A which receives a pin 31 firmly secured to the machine frame 1, so that side plate 30 is guided for elevational motion by slot 30 and pin 31. Firmly secured to an upper portion of side plate 30 is a follower pin 32 which is maintained in engagement with a cam 34 mounted on a shaft 33. Shaft 33 is rotated by drive means 35 through gearing 36 attached to its output shaft 35a. Rotation of cam 34 by shaft 33 moves side plate 311 upwardly and hence developer supplementing pan 19 to its upper position in which a dry developer 22 in powder form is supplied to the magnet units 21.

From the foregoing description, it will be appreciated that with a developing device according to this invention an electrostatic latent image is developed on a photosensitive sheet while the sheet is moving through the developing section without requiring a sheet receiver, sheet hold-down frame or other supporter. Because of this, the developing device according to this invention is not limited to developing any particular size or sizes of photosensitive sheets. Besides, if an electrically conducting rubber belt is used as the endless belt of the photosensitive sheet conveyor means, it will be possible to impress a bias voltage on the photosensitive sheet safely and effectively without the fear of short-circuiting, regardless of the size of the sheet on which a latent image to be developed is formed, thereby making it possible to produce a well-defined, clearly visible image with minimized fog in the background (background density).

What we claim is:

1. A developing device of the brush type for electrophotographic apparatus using a dry developer comprising pivotal magnet units for forming on the undersides thereof a magnetic brush composed of a dryer developer in powder form, a developer supplementing pan disposed beneath said magnet units and containing therein a quantity of a dry developer in powder form for delivering a fresh supply of such dry developer to said magnet units, means for moving said developer supplementing pan and said magnet units toward and away from each other in relative movements, and photosensitive sheet conveyor means interposed between said magnetunits and said developer supplementing pan, said photosensitive sheet conveyor means being in the form of movable endless belt means which can move between a developing position and a retracted position so that the magnet units and the developer supplementing pan can move in relative movements while said endless belt means is disposed in its retracted position.

2. A developing device as defined in claim 1 wherein said movable photosensitive sheet conveyor means moves in the same direction as the direction of movement of exposed photosensitive sheets when the photosensitive sheet conveyor means moves from its retracted position to its developing position.

3. A developing device as defined in claim 2 wherein the endless belt of said movable photosensitive sheet conveyor endless belt means is driven to move upon restoration of the movable photosensitive sheet conveyor means to its developing position.

4. A developing device for electrophotographic apparatus using a dry developer comprising:

a. means containing a supply of dry developer powder;

- b. magnetic means disposed above said supply means and having an under surface on which a magnetic brush composed of dry developer power is formed;

0. conveyor means for passing photosensitive sheets containing latent images thereon beneath said magnetic means for developing by said magnetic brush;

d. means for bringing said magnetic means and said supply means together after developing for replenishing dry developer powder of said magnetic brush; and

e. means for retracting said conveyor menus from heneath said magnetic means during replenishing to avoid obstructing the relative movement between said magnetic means and said supply means.

5. A device as in claim 4, including means for driving said conveyor means when beneath said magnetic means.

6. A device as in claim 4, wherein said means for bringing said magnetic means and said supply means together comprises:

f. means fixed to said supply means having a slot therein;

g. means fixed to said electrophotographic apparatus riding in said slot;

h. follower means on said slotted means;

i. cam means on which said follower means rides; and

j. means for driving said cam means to cause said follower to raise and lower said slotted means whereby said supply means is raised and lowered with respect to the electrophotographic apparatus.

7. A device as in claim 6, including means for agitating said supply of dry developer powder when said supply means is in its lowered position.

8. A device as in claim 4, including means for agitating said magnetic means during developing.

9. A device as in claim 8, wherein said agitating means comprises:

f. two parallel support shafts;

g. first link means for fixedly connecting said magnetic means to one of said shafts;

h. second link means for loosely connecting said magnetic means to the other of said shafts;

i. rocker means connected to the ends of said shafts;

j. means for driving said rocker means to cause said magnetic means to execute an agitating motion.

10. A device as in claim 4, wherein said magnetic means comprises:

f. a plurality of juxtaposed magnetic cases having flat surfaces on their undersides;

g. a magnet in each case producing a magnetic field on the underside for holding the dry developing power thereon;

h. means for relatively moving said magnets and said flat surfaces away from each other after developing to degrees the magnetic field on said flat surfaces to drop the dry developer powder therefrom. 

1. A developing device of the brush type for electrophotographic apparatus using a dry developer comprising pivotal magnet units for forming on the undersides thereof a magnetic brush composed of a dry developer in powder form, a developer supplementing pan disposed beneath said magnet units and containing therein a quantity of a dry developer in powder form for delivering a fresh supply of such dry developer to said magnet units, means for moving said developer supplementing pan and said magnet units toward and away from each other in relative movements, and photosensitive sheet conveyor means interposed between said magnet units and said developer supplementing pan, said photosensitive sheet conveyor means being in the form of movable endless belt means which can move between a developing position and a retracted position so that the magnet units and the developer supplementing pan can move in relative movements while said endless belt means is disposed in its retracted position.
 2. A developing device as defined in claim 1 wherein said movable photosensitive sheet conveyor means moves in the same direction as the direction of movement of exposed photosensitive sheets when the photosensitive sheet conveyor means moves from its retracted position to its developing position.
 3. A developing device as defined in claim 2 wherein the endless belt of said movable photosensitive sheet conveyor endless belt means is driven to move upon restoration of the movable photosensitive sheet conveyor means to its developing position.
 4. A developing device for electrophotographic apparatus using a dry developer comprising: a. means containing a supply of dry developer powder; b. magnetic means disposed above said supply means and having an under surface on which a magnetic brush composed of dry developer power is formed; c. conveyor means for passing photosensitive sheets containing latent images thereon beneath said magnetic means for developing by said magnetic brush; d. means for bringing said magnetic means and said supply means together after developing for replenishing dry developer powder of said magnetic brush; and e. means for retracting said conveyor means from beneath said magnetic means during replenishing to avoid obstructing the relative movement between said magnetic means and said supply means.
 5. A device as in claim 4, including means for driving said conveyor means when beneath said magnetic means.
 6. A device as in claim 4, wherein said means for bringing said magnetic means and said supply means together comprises: f. means fixed to said supply means having a slot therein; g. means fixed to said electrophotographic apparatus riding in said slot; h. follower means on said slotted means; i. cam means on which said follower means rides; and j. means for driving said cam means to cause said follower to raise and lower said slotted means whereby said supply means is raised and lowered with respect to the electrophotographic apparatus.
 7. A device as in claim 6, including means for agitating said supply of dry developer powder when said supply means is in its lowered position.
 8. A device as in claim 4, including means for agitating said magnetic means during developing.
 9. A device as in claim 8, wherein said agitating means comprises: f. two parallel support shafts; g. first link means for fixedly connecting said magnetic means to one of said shafts; h. second link means for loosely connecting said magnetic means to the other of said shafts; i. rocker means connected to the ends of said shafts; j. means for driving said rocker means to cause said magnetic means to execute an agitating motion.
 10. A device as in claim 4, wherein said magnetic means comprises: f. a plurality of juxtaposed magnetic cases having flat surfaces on their undersides; g. a magnet in each case producing a magnetic field on the underside for holding the dry developing power thereon; h. means for relatively moving said magnets and said flat surfaces away from each other after developing to degrees the magnetic field on said flat surfaces to drop the dry developer powder therefrom. 